For the problem that TACAN airborne equipment is huge in analog system and that the calculating method of TACAN bearing signal is complex in calculating process and low in precision ,this paper presents an accurate method of calculating the bearing settlement using Kalman filtering distill envelope signal based on the ideal of software radio and IF digital processing .Firstly, this paper adopts the method of state space description to derive in detail the expressions of various parameters in the observation equation and state equation of envelope signal, then, designs the Kalman filtering model of distill envelope signal，extracts the envelope signal process and the method of calculating bearing. Finally, the experiment result of equipment simulator shows that the designed method is simple in process, accurate in calculating bearing precision and is applicable to the practical equipment.